Gabe Newell gives you his Steam account information, dares you to steal it.

Valve is so confident in its new Steam Guard technology, that Gabe Newell is giving you his username and password to try and steal his Steam account. Steam Guards ties your Steam account to your Intel based PC, making it so that the only PC that can login to Steam will be the one you specify. If you're worried about someone stealing your Steam account, then you might want to use Steam Guard.

This begs the question though, would you even need to login if you are using Steam Guard? I guess if you want to keep anyone in your household from playing without logging in, that would be a reason to keep the login functionality. Anyways, here's Gabe giving you his username and password. See if you can login as him and reap the rewards all the games in his library.